Activation of ERK in renal fibrosis after unilateral ureteral obstruction: modulation by antioxidants

Vitamins C and E attenuate apoptosis, beta-adrenergic receptor desensitization, and sarcoplasmic reticular Ca2+ ATPase downregulation after myocardial infarction

Oxidative stress plays an important role in mediating ventricular remodeling and dysfunction in heart failure (HF), but its mechanism of action has not been fully elucidated. In this study we determined whether a combination of antioxidant vitamins reduced myocyte apoptosis, beta-adrenergic receptor desensitization, and sarcoplasmic reticular (SR) Ca2+ ATPase downregulation in HF after myocardial infarction (MI) and whether these effects were associated with amelioration of left ventricular (LV) remodeling and dysfunction. Vitamins (vitamin C 300 mg and vitamin E 300 mg) were administered to rabbits 1 week after MI or sham operation for 11 weeks. The results showed that MI rabbits exhibited cardiac dilation and LV dysfunction measured by fractional shortening and the maximal rate of pressure rise (dP/dt), an index of contractility. These changes were associated with elevation of oxidative stress, decreases of mitochondrial Bcl-2 and cytochrome c proteins, increases of cytosolic Bax and cytochrome c proteins, caspase 9 and caspase 3 activities and myocyte apoptosis, and downregulation of beta-adrenergic receptor sensitivity and SR Ca2+ ATPase. Combined treatment with vitamins C and E diminished oxidative stress, increased mitochondrial Bcl-2 protein, decreased cytosolic Bax, prevented cytochrome c release from mitochondria to cytosol, reduced caspase 9 and caspase 3 activities and myocyte apoptosis, blocked beta-adrenergic receptor desensitization and SR Ca2+ ATPase downregulation, and attenuated LV dilation and dysfunction in HF after MI. The results suggest that antioxidant therapy may be beneficial in HF.

Pathogenesis of renal injury in obstructive uropathy

PURPOSE OF REVIEW

This review focuses on recent advances in understanding the factors contributing to obstructive nephropathy, the most important cause of renal failure in children. The major focus is on renal cellular and molecular events, with emphasis on those affecting the developing kidney.

RECENT FINDINGS

Experiments in the fetal sheep or neonatal rat, mouse, or pig reveal dramatic effects of urinary tract obstruction on renal growth and development. Surgical relief of obstruction can reverse some of the structural and functional deficits, but cannot restore normalcy. Renal tubular apoptosis is a major factor leading to tubular atrophy following unilateral ureteral obstruction. Increased reactive oxygen species, and a renal environment favoring pro-apoptotic, over survival, signals, contribute to cell death. A variety of intrarenal factors lead to progressive interstitial fibrosis, including the newly described process of epithelial-mesenchymal transition, whereby tubular epithelial cells are transformed into activated fibroblasts. A number of endogenous antifibrotic counter-regulatory molecules have been identified, opening the possibility of enhancing the kidney's own defenses against progressive fibrosis.

SUMMARY

The renal response to urinary tract obstruction is complex and involves a wide array of interacting molecules. Elucidation of these interactions will lead to the identification of biomarkers that will allow a more precise prediction to the response to surgical intervention and, hopefully, to novel therapies to prevent renal deterioration.

Aldosterone Stimulates Collagen Gene Expression and Synthesis Via Activation of ERK1/2 in Rat Renal Fibroblasts

Recently, we demonstrated that in rats treated chronically with aldosterone and salt, severe tubulointerstitial fibrosis is associated with the activation of mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinases (ERK1/2). Here, we investigated whether aldosterone stimulates collagen synthesis via ERK1/2-dependent pathways in cultured rat renal fibroblasts. Gene expression of mineralocorticoid receptor (MR) and types I, II, III, and IV collagen was measured by real-time polymerase chain reaction (PCR). MR protein expression and ERK1/2 activity were evaluated by Western blotting analysis with anti-MR and anti–phospho-ERK1/2 antibodies, respectively. Collagen synthesis was determined by [ 3 H]-proline incorporation. Significant levels of MR mRNA and protein expression were observed in rat renal fibroblasts. Treatment with aldosterone (0.1 to 10 nmol/L) increased ERK1/2 phosphorylation in a concentration-dependent manner with a peak at 5 minutes. Aldosterone (10 nmol/L) also increased the mRNA levels of types I, III, and IV collagen at 36 hours but had no effect on the type II collagen mRNA level. [ 3 H]-proline incorporation was significantly increased by aldosterone in both the medium and cell layer at 48 hours. Aldosterone-induced ERK1/2 phosphorylation was markedly attenuated by pretreatment with eplerenone (10 μmol/L), a selective MR antagonist, or PD98059 (10 μmol/L), a specific inhibitor of MAPK kinase/ERK kinase, which is the upstream activator of ERK1/2. In addition, both eplerenone and PD98059 prevented the aldosterone-induced increases in types I, III, and IV collagen mRNA and [ 3 H]-proline incorporation. These results suggest that aldosterone stimulates collagen gene expression and synthesis via MR-mediated ERK1/2 activation in renal fibroblasts, which may contribute to the progression of aldosterone-induced tubulointerstitial fibrosis.